This proposal is based upon our intriguing observation in piglets that oxygen free radicals are responsible for attenuated cerebrovascular responses to N-Methyl-D-Aspartate (NMDA), a substance which dilates by a mechanism involving enhanced nitric oxide (NO) production by cortical neurons. However, precise details concerning mechanisms of action of oxygen radicals are unclear. Based upon our findings and those int eh literature we propose the following hypotheses: a) Oxygen radicals alter cortical NMDA receptor characteristics; B) Oxygen radicals cause generalized "stunning" of neurons and thus impaired synthesis of NO; C) Oxygen radicals inhibit activation of NO synthase (NOS); D) Continued oxygen radical production inactivates NO before it can reach vascular smooth muscle; E) Oxygen radicals inhibit function of receptors for calcitonin gene-related peptide; F) Oxygen radicals inhibit vascular responses dependent on guanylate cyclase; and G) Attenuated responsiveness to NMDA or glutamate occurs in other areas such as cerebellum. To test these hypotheses, two specific aims will be addressed using newborn pigs; 1. CHARACTERIZATION OF ASPHYXIA/REVENTILATION-INDUCED CHANGES IN CEREBROVASCULAR RESPONSIVENESS; AND 2. DETERMINATION OF MECHANISMS OF ASPHYXIA/REVENTILATION-INDUCED CHANGES IN CEREBROVASCULAR RESPONSIVENESS. We will use a number of complimentary methods for characterizing vascular and neuronal responses. These include the closed cranial window and intravital microscopy for characterization of responses of individual arteries and arterioles, the 14C-deoxyglucose method for determination of brain glucose utilization, in vitro measurement of NOS activity by L- arginine to L-citrulline conversion, measurement of cortical NO production by microdialysis, determination of superoxide anion production using the superoxide dismutase-inhibitable nitroblue tetrazolium method, and receptor binding determinations for numbers and affinities of NMDA receptors. This investigation will explore control mechanisms in neonatal animals during normal and pathophysiological conditions. We hope that our findings will be of clinical relevance and lead to therapies that improve outcome in stressed babies.